For the purpose of global environmental protection, it has been promoted to improve fuel economy of automobiles. Thus, automobile tires having less rolling resistance are also desired.
Rolling resistance of a tire is largely attributable to by energy loss caused by the repeated deformation of the tire during running. In order to reduce rolling resistance, it is suggested that, for example, a rubber tread portion, which more largely contributes to rolling resistance than any other tire component, be formed to have a two-layer structure in which a rubber composition with small energy loss is provided on the inner side (base tread) and a rubber composition excellent in abrasion resistance is provided on the outer side (cap tread).
Generally, reducing the energy loss of a cap tread rubber causes the problems of reduced grip performance, poor abrasion resistance and poor cut and chip resistance. Further, in the case of using a modified polymer for silica formulations to reduce the energy loss, a large amount of the polymer deteriorates processability. Also if the amount of reinforcing agent is reduced to reduce the energy loss, then the rigidity tends to be reduced and the handling stability (handling performance) tends to be deteriorated. As described above, it is difficult for a cap tread rubber to improve in handling stability, abrasion resistance, and fuel economy in a balanced manner, and it is also difficult to obtain a good balance of wet grip performance and processability.
For example, Patent Literature 1 discloses a rubber composition including a modified styrene-butadiene rubber, silica, and the like so as to improve properties such as fuel economy. However, it still has room for improvement in the properties described above in a balanced manner.